When a jumpstart goes wrong?

[u/jhwalk09]

Neighbor tried jumping my wife’s ‘06 Nissan Altima, we left it for 10 minutes and came back and the cables had melted through the headlight of both cars and some of the bumper. I wasn’t there but thankfully they stopped their car and were able to disconnect the cables without incident. We noticed after there had been mice living in around her engine from the mouse poop, minimum the last two weeks. What causes jumper cables to do this? Something a rodent may have chewed? Definitely an issue with my wife’s car. Our poor neighbors have a newish midsized suv. My wife has also had constant issues starting her car, even with a new battery I got a year or two ago. Anyone seen this before?

[u/Contristatus → u/[deleted]]

the negative terminal and the chassis are continuous, it's the same amount of current both ways (as long as the polarity is right) but using a chassis ground eliminates the small chance of a spark igniting the gasses produced when charging a battery

[u/GrumpyDumping → u/Contristatus]

Connecting the two sets of battery terminals together wrong could cause a dead short (an electrical circuit with lots of amperage but very little resistance), cause sparking, melt your jumper cables and possibly damage [the batteries and electronic systems of both vehicles.

https://www.familyhandyman.com/project/how-to-jump-start-your-car-safely/#:~:text=Connecting%20the%20two%20sets%20of,electronic%20systems%20of%20both%20vehicles.

[u/jepulis5 → u/GrumpyDumping]

Are you AI-based or is your reading comprehension really that bad?

[u/evoke3 → u/jepulis5]

Dude just absolutely destroyed himself. He could have found countless sources saying to connect to ground but he chose one that specifically says he is wrong.